1. Field of the Invention
This invention relates in general to circuit breaker trip crossbars and more particularly to an improved pivot means or method for forming a pivot for a circuit breaker trip crossbar.
2. Summary of the Prior Art
Trip crossbars utilized in circuit breakers usually carry a metal latch plate for latching the contact resetting or operating assembly of the circuit breaker. The assembly can then be operated for moving and holding the contacts in closed position and when the bar is rotated in response to a fault condition, the latch plate is disengaged from the operating assembly which opens or restores the circuit breaker contacts.
The crossbar is an elongated molded plastic member having axially spaced arcuate bottom surfaces each pivotally engaged with the edge of a respective wedge shaped recess formed in a respective compartment or barrier wall of the breaker. The arcuate surfaces are actually formed on an eccentric portion of the bar, which requires a relative deep wide wall recess to accommodate rotation of the eccentric portion. This renders encircling restraint of the crossbar difficult to provide.
The arcuate surfaces being displaced from the crossbar axis of rotation and having relatively large area of engagement require a relatively large torque to overcome the friction between the bar and recess edges, while the minimal encircling restraint contributes to the friction and wear problems of the bar. It also renders calibration difficult since each rotational movement of the bar may vary from the others.
The wear, friction and calibration problems are further complicated by the necessity to apply the forces for pivoting or tripping the bar in response to a fault condition at asymmetrical locations with respect to the inadequately restrained crossbar resulting in eccentric movement of the bar relative to the support surfaces of the recess further complicating the force, wear and calibration problems.
The metal latch plate is secured to the crossbar by a rivet passing through a hole in the arm extending transverse to the elongate bar axis. For economical molding of the hole in the bar, one mold half may carry a pin and form the hole and the opposite halves of the mold engage along parting lines spaced angularly substantially 90.degree. from the hole axis and extending along the arcuate or pivot surfaces of the bar. Parting lines may in some instances also be formed along the barrier wall recess edges that engage the pivot surfaces of the bar. The parting lines create some flash along the pivot surfaces which is inordinately expensive to remove. The flash introduces contaminants between the pivot surfaces and creates a variable load resisting crossarm pivoting. This further contributes to the problem of calibrating the tripping forces required to release the reset or operating assembly.